U.S. forces paused Thursday for moments of silence across Iraq, as part of several ceremonies marking the anniversary.
Civilian administrator L. Paul Bremer and Lt. Gen. Ricardo Sanchez, the commander of U.S. ground forces in Iraq, attended a memorial at the former Republican Palace in Baghdad, along with about 400 other members of the Coalition Provisional Authority.
The chaplain, Col. Frank Wisner, said a few words before a moment of silence, followed by "Amazing Grace," played by a British soldier on bagpipes.
"In the eternal silence of the shared moments, let us attune our hearts to the voices crying out from September 11th, 2001, compelling us to eradicate terrorism in our world and to restore justice and dignity to creation," Wisner said.
Memorial services were also held in Tikrit -- Saddam Hussein's hometown -- and during a prayer breakfast at Baghdad's International Airport.
Speaking at the Tikrit memorial, Gen. Ray Odierno urged the soldiers not to forget the victims of September 11, and the servicemen and women who have died in Afghanistan and Iraq.
"Those soldiers, airmen, sailors, Marines, civilians who have given their life for a better life not only for people in the U.S., but here in Iraq," Odierno said.
"It is our job to ensure that we maintain this freedom for years to come, for our children. For our children's children. This is why we are here. And it will make a difference."
In Sydney, Australia, United States consulate staff members planted 3,000 trees in an inner city park, and embassy staff in the capital, Canberra, will light candles on the U.S. Embassy grounds Thursday evening.
The candles -- one for each life lost in the September 11 attacks -- will be lit at 10.46 p.m. local time, to coincide with the time the first plane hit the World Trade Center.
U.S. Embassy and consulate staff around Australia also encouraged people to mark the anniversary by volunteering in their communities.